In U.S. Pat. No. 3,986,030 there is disclosed a device for impinging a light ray, preferably within a region of the spectrum not visible to the human eye, such as an infra-red ray, onto the cornea of the human eye, which is reflected therefrom and directed by eye movement onto a particular key of a keyboard, a photo-electric converter converting the light ray impinging on the selected key to strike the latter, if, and only if, an additional activating signal is concurrently received by the mechanism, the additional activitating signal being commanded, for example, by the suction of the operator on a specially fitted hose. The aforementioned device suffers from the disadvantage that a light ray reflected from the cornea is diffuse and not collimated or focused, so that, unless the keys of the keyboard are widely spaced apart, there is a risk of activating neighboring keys, in addition to a desired key. The need has therefore arisen to find a way of focusing the cornea-reflected light rays directly on the selected key of he keyboard, even if the keys of the keyboard are spaced closely to one another.